1. Field of the Invention
The present invention relates to a sheet storing apparatus which stores sheets having images formed thereon by an image forming apparatus at a stack tray directly or after performing a binding process with collating and stacking.
2. Description of Related Arts
In general, in such a sheet storing apparatus, an image sheet fed out from a main body apparatus such as an image forming apparatus is guided to a sheet discharging path and is stored at a stack tray which is arranged downstream of the sheet discharging path. Then, a lifting mechanism is arranged to lift and lower the stack tray in a stacking direction in accordance with a stacked amount of sheets. Further, a stack level detecting mechanism which detects a height position of the upmost sheet stacked on the stack tray is arranged to control the lifting mechanism.
For example, Japanese Patent Application Laid-Open No. 2009-035371 (Patent Document 1) discloses a sheet storing apparatus in which a sheet having an image formed thereon by an image forming apparatus is conveyed to a post-processing apparatus arranged downstream of a sheet discharging port and is stored at a stack tray arranged in the apparatus.
In Patent Document 1, the storing apparatus includes a sheet introducing path which introduces a sheet from the image forming apparatus, a processing tray which is arranged downstream of the sheet introducing path, and a stack tray which is arranged downstream of the processing tray. The processing tray is provided with an aligning mechanism which performs positioning of a sheet through a sheet discharging port to a predetermined processing position with switching-back, and a stapling unit which binds collated and stacked sheets.
Further, the stack tray is located downstream of the abovementioned sheet introducing path and is provided with a tray member which is located downstream of the processing tray and a lifting-lowering mechanism which lifts and lowers the tray member in the stacking direction.
Then, a sheet discharging path for discharging a sheet directly to the stack tray from the introducing path (print-out discharging) and a sheet discharging path for discharging a sheet bundle binding-processed at the processing tray (staple-binding discharging) are formed in accordance with a mode specified by the main body (a copying machine, a computer apparatus, or the like).
With such a sheet storing mechanism to lift and lower the stack tray in accordance with a stacked amount of sheets, it is required to detect a height level of the upmost sheet on the stack tray.
As such a level detecting mechanism, there have been known a configuration to perform the detection while a sensor detects a height position of a sheet holding member which is arranged to be movable between an operation position above the stack tray and a waiting position outside the stack tray and a configuration to include, at a side above tray, a light emitting element which radiates beam light to path through the sheet discharging path and a light receiving element which receives the light.
In Japanese Patent No. 4057233 (Patent Document 2), a sheet discharged from an image forming apparatus is stored at a stack tray while being provided with a mechanism to detect a height position of stacked sheets with a sheet-contact lever and a photo-sensor which detects an angle position of the sheet-contact lever and a conveying rotor which performs aligning by causing sheets discharged through a sheet discharging port to be abutted to a sheet end reference face of the stack tray. Here, a rotation force is transmitted to the conveying rotor so that a tailing end of a sheet fed by a sheet discharging roller is drawn to the reference face of the stack tray.
Further, in such an apparatus, there has been widely known a sheet storing apparatus having a jog function to perform storing with offsetting of a sheet discharging path or a storage tray by a predetermined amount in a direction perpendicular to a sheet discharging direction, when a sheet is to be stored at a storage tray arranged at the downstream side from the sheet discharging path.
For example, Japanese Patent Application Laid-Open No. 2002-012362 (Patent Document 3) discloses a sheet storing apparatus which stores a sheet from a sheet discharging path to a processing tray and a jog mechanism which offsets a stack tray by a predetermined amount laterally in a direction perpendicular to the sheet discharging direction while being capable of vertically moving the stack tray in the stacking direction.
In a sheet storing apparatus including a lifting-lowering mechanism and a jog mechanism of a stack tray as described above, the lifting-lowering mechanism is controlled to detect a height level of sheets stored at the stack tray, and when the height level arrives at a predetermined value, to lower the sheet height level by lowering the stack tray.
Further, when a jogging operation is mode-selected by an upstream apparatus (e.g., an image forming apparatus, or the like) and a sheet discharge instruction signal for the first sheet is received, the stack tray is controlled to be moved in the sheet width direction.
In such an apparatus configuration, there is a case that instruction signals for a tray lifting operation and a jogging operation are concurrently provided. There is no disclosure about execution timing of the tray lifting-lowering operation and the tray jogging operation with the apparatus in Patent Document 3.
Regarding execution timing of co-occurring operations, for example, when an operator removes stacked sheets from the stack tray, the apparatus performs the lifting operation of the stack tray as detecting the height level of sheets. When a sheet is discharged through a sheet discharging port at that time, there is a case that the sheet falls outside the stack tray.
Further, during an operation in a jog mode, a jog instruction signal of continuously-discharged sheets is provided and a sheet is discharged thereafter.
In a conventional apparatus, when stacked sheets are carelessly removed from a stack tray, based on detection of the above by a level sensor, a sheet discharging operation is restarted after the stack tray is lifted to an appropriate position with the sheet discharging operation stopped.
In general, such an image forming system configuration has been known as a system which stores sheets having images formed thereon in a duplex manner by an image forming unit at a downstream stack tray after performing a post-process as stacking the sheets to a processing tray which is arranged at a post-processing unit.
In such a system, there has been known a system configuration in which a post-processing unit is arranged above an image forming unit and the post-processing unit includes a stack tray and a guide tray of a duplex path for duplex printing at the upper and lower sides thereof, as disclosed in Japanese Patent No. 3752172 (Patent Document 4), for example.
Patent Document 4 also discloses a system configuration including a duplex path on which a sheet having an image formed at one side by an image forming unit is temporarily discharged to the post-processing unit and is fed again to the image forming portion as being switched back.
Patent Document 4 proposes an apparatus structure in which an post-processing apparatus is arranged above an image forming apparatus, the stack tray of the post-processing apparatus is structured with a lifting-lowering tray which vertically moves in a stacking direction, and a switch-back path for face-reversing a sheet fed from the image forming portion is formed below the vertically-moving lifting-lowering tray.
In Patent Document 4, the guide tray which forms the switch-back path is formed at a wide angle inclined gentler than a sheet placement face of the stack tray. Further, Patent Document 4 discloses a mechanism with which a sheet fed from the image forming apparatus is face-reversed at the switch-back path located at the lower side and the stack tray is lifted and lowered at the upper side.